The present invention relates generally to medical/surgical devices, systems and methods. More specifically, the invention relates to devices, systems and methods for enhancing a knee surgery procedure.
Total knee replacement surgery, also referred to as total knee arthroplasty (“TKA”), is becoming an increasingly important treatment for chronic knee pain and joint dysfunction. A recent panel of the National Institutes of Health at a Consensus Development Conference recognized that approximately 300,000 TKA surgeries are performed annually in the U.S. for end-stage knee arthritis. The NIH panel agreed that although advances have been made in TKA surgical devices and techniques, improved outcomes through further innovations should still be diligently pursued. The panel concluded that techniques for placing artificial knee prostheses, in particular, should be improved to provide better outcomes and reduce wear of the prostheses, to thus reduce the need for repeat TKA surgeries. If advances in TKA continue to be made, the procedure may become more readily available to younger patients, obese patients, and the like, who may need TKA but who do not fall within in the “ideal” age range traditionally defined as between 60 and 75 years old. Improved techniques and devices would also mean enhanced outcomes for all TKA patients, with better functioning of the knee joint and longer useful life of the prosthetic knee.
The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues within and surrounding the knee joint. Four ligaments are especially important in the functioning of the knee—the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia has been worn away to allow the femur to directly contact the tibia. This bone-on-bone contact causes significant pain and discomfort. The primary goals of a TKA procedure are to replace the distal end of the femur, the proximal end of the tibia, and often the inner surface of the patella with prosthetic parts to avoid bone-on-bone contact and provide smooth, well-aligned surfaces for joint movement, while also creating a stable knee joint that moves through a wide range of motion.
One of the greatest challenges in TKA surgery is to properly balance ligament tension, especially in the medial and lateral collateral ligaments, through a full range of motion of the knee. The collateral ligaments, which connect the distal femur and proximal tibia on the medial and lateral aspects of the knee, account for much of the stability and movement of the knee. If one of the collateral ligaments is too lax or too tight relative to the other collateral ligament, the knee will typically be unstable, range of motion may be limited, the patella may track improperly, and the femur and/or tibia may wear unevenly, leading to arthritis and pain. Uneven ligament tension after TKA surgery will typically cause joint instability and poor patellar tracking, limited range of motion, and impaired function of the knee, as well as uneven, increased wear of the prosthetic device, which often necessitates repeat surgery. Thus, it is imperative for the short- and long-term success of a TKA procedure to achieve balanced ligament tension in the knee through a full range of motion.
Balancing ligament tension during TKA surgery is complicated by the fact that the natural knee does not operate like a hinge moving about a single axis. The knee exhibits dynamic external rotation of the tibia relative to the femur as the knee moves from its flexed to its fully extended position. This automatic rotation of the tibia occurs in the opposite direction when the knee is flexed from its fully extended position to produce an internal rotation of the tibia relative to the femur. Thus, the natural knee exhibits a rotary laxity that allows the tibia to rotate through a limited internal and external arc, during knee flexion. Additionally, the femur translates anteriorly and posteriorly as the tibia is being flexed about it, bringing yet another movement variable into the equation. Thus, the ligaments of the knee, along with the femur, tibia and patella, create a truly dynamic bio-mechanism, making ligament tension balancing in TKA surgery extremely challenging. Many articles and studies have been devoted to ligament tension balancing in TKA, such as the following: Mihalko, W H et al., “Comparison of Ligament-Balancing Techniques During Total Knee Arthroplasty,” Jnl. Bone & Jt. Surg., Vol. 85-A Supplement 4, 2003, 132-135; Eckhoff, DG et al., “Three-Dimensional Morphology and Kinematics of the Distal Part of the Femur Viewed in Virtual Reality, Jnl. Bone & Jt. Surg., Vol. 85-A Supplement 4, 2003, 97-104; and Ries, MD, et al., “Soft-Tissue Balance in Revision Total Knee Arthroplasty,” Jnl. Bone & Jt. Surg., Vol. 85-A Supplement 4, 2003, 38-42.
One technique for balancing collateral ligament tension during a TKA procedure involves cutting fibers of one or both ligaments to decrease ligament tension—a technique referred to as “ligament release.” Although ligament release is still commonly used, the disadvantage of this technique is that it requires actually cutting ligament tissue, thus weakening the ligament(s) and leaving less room for error if future releases or TKA procedures are required.
Rather than or in addition to ligament release, the components of a total knee prosthesis may be selected and positioned to balance ligament tension. Since the femoral and tibial components of the prosthesis are attached to cut surfaces of the distal femur and proximal tibia respectively, placement and orientation of the bone cuts are also critically important. Typically, the tibial component of the prosthesis is positioned on a flat, horizontal cut surface of the proximal tibia (at a 90 degree angle relative to the long axis of the tibia), and the position and orientation of the tibial component typically do not vary greatly from knee to knee. Therefore, most of the variation in positioning of the total knee prosthesis typically occurs in positioning the femoral component and the femoral bone cuts. The surgeon attempts to make these femoral bone cuts to achieve a position and orientation of the femoral prosthetic component so as to optimally balance ligament tension through a full range of motion of the knee. As with ligament release however, it is often very challenging to position the femoral bone cuts and femoral prosthetic component to provide ideal ligament tension through the range of motion. This is due primarily to the complexity of motion about the knee, as described above, and the difficulty of placing the femoral component so as to maintain desired ligament tension through the full range of motion. Specifically, the rotational, proximal/distal and anterior/posterior orientations and locations of the femoral component are all critical for duplicating the kinematics of the knee.
In a typical TKA procedure, multiple cuts are made to the distal femur before attaching the femoral component of the prosthesis. Most procedures, for example, involve making a distal cut across the distal end of the femur, anterior and posterior cuts, and angled anterior and posterior chamfer cuts to help secure the femoral component solidly in place. In order to effectively and accurately make these resections, orthopedic surgeons typically use a cutting block or cutting guide, used to guide a surgical saw blade or rotary tool, which is temporarily attached to the distal end of the femur. Positioning of such a cutting block, therefore, is crucial to forming well-positioned bone cuts for attachment of the femoral prosthetic component.
A number of devices and techniques have been described that attempt to facilitate ligament balancing during a TKA procedure. Some techniques, such as those described in U.S. Pat. No. 5,733,292, involve trial prosthesis components which are used after femoral and tibial bone cuts are made to assess ligament tension. Some devices, such as those described in U.S. Patent Application Publication No. 2003/0187452, are used to measure a gap between the distal femur and proximal tibia in extension and to help a surgeon recreate that same gap when the knee is in flexion. Other “gap checking” devices are described in U.S. Pat. No. 6,575,980. Other devices have been developed to help measure an amount of ligament tension or to apply a desired amount of tension to the ligaments. U.S. Pat. No. 4,501,266, for example, describes a knee distraction device for applying a desired amount of tension. Many paddle-like devices have been suggested for applying or measuring tension across a knee joint, such as the devices described in U.S. Pat. Nos. 5,597,379; 5,540,696; 5,800,438; 5,860,980; 5,911,723; and 6,022,377.
One proposed alternative to the cutting block technique for making bone cuts on a distal femur involves the use of robotic surgical systems for making distal femoral bone cuts. With robotic surgery and surgical navigation, a surgical saw blade or bur is still used, but the bone cuts are positioned as a result of fiducial-based or shape-based registration of the patient's anatomy. In fiducial-based approaches, fiducials, or markers are attached to pertinent anatomical structures prior to imaging. During surgery, the markers are exposed, and a sensor system conveys their location to the computer. A wide variety of sensing systems available, including optical trackers, electromagnetic transceivers, articulated probe arms, and ultrasonic and laser range finders. In shape-based approaches, the shapes of anatomical structures are fitted to preoperative image data. The patient measurements can be obtained from a variety of sensing techniques, including tracing curves, scanning distances, or processing images, via one or some of the aforementioned sensing systems. One description of the use of robotic surgery systems in knee surgery procedures is found in Howe, R D, and Matsuoka, Y, “Robotics for Surgery,” Annu. Rev. Biomed. Eng. 1999, 01:211-240.
Although some of the devices and techniques described above have helped enhance and facilitate TKA procedures, currently available devices and techniques still have a number of shortcomings. Most importantly, currently available devices do not allow a physician to adjust ligament tension in a knee and also receive positional information based on that adjustment that can be used to facilitate completion of the TKA surgery. For example, many currently available devices are applied only in extension or only in flexion of the knee, or must be removed and replaced when the knee is moved from extension to flexion. Thus, it is difficult or impossible to assess ligament tension through the full range of motion using many currently available devices. Some devices rely on measuring a gap or amount of tension in extension and then recreating the gap or tension in flexion. Again, this does not always result in collateral ligament balance throughout the range of motion. Still other devices are very cumbersome and/or complex. Many include large parts which fit external to the knee joint and necessitate the patella being moved to the side during measurement or other phases of the TKA procedure. Furthermore, current devices typically do not reside primarily within the joint space during a surgical procedure to allow for the natural movements, rotations and translations of the tibia and femur as the knee is flexed through a range of motion. In some techniques, bone cuts are made before ligament balancing is achieved, thus often requiring re-cutting of those same bone cuts. More bone cuts mean more trauma to the patient, a longer recovery period, and less bone to work with if a second TKA is required later in life.
Although robotic surgery may provide a level of improvement over more traditional techniques, it is typically difficult or impossible using current robotic techniques to dynamically mark or register and sense the proper dynamic position to make well-positioned, subsequent bone cuts for attachment of the femoral prosthetic component. Thus, even with robotic systems, it is still challenging to achieve a desired ligament balance to enhance knee stability, range of motion and patellar tracking. These and other shortcomings of currently available devices and methods continue to make ligament balancing, and specifically collateral ligament balancing, one of the most challenging aspects of TKA surgery.
Therefore, a need exists for improved devices, systems and methods for enhancing TKA surgery and specifically for dynamically balancing ligaments during TKA to improve range of motion, stability, and patellar tracking of the prosthetic knee joint. Ideally, such devices would help a surgeon balance ligaments dynamically, through a full range of motion of the knee, allowing for the natural rotation of the tibia and the natural translation of the femur while the tibia is being flexed about it. Also ideally, such devices and methods would allow a surgeon to achieve a desired ligament tension balance before committing to and making final bone cuts to the femur. Such devices would ideally be simple to use in conjunction with cutting guides, saw blades or burs, and robotic and navigational systems, preferably allowing the patella to remain in place during assessment of ligament tension. At least some of these objectives will be met by the present invention.